Removal of pyritic sulfur from coal using solutions containing ferric ions

ABSTRACT

Finely divided coal or solid coal derivatives containing pyrite are reacted with a ferric ion solution; FeCl3 is particularly suitable. The ferric ion is reduced to ferrous ion and free sulfur is formed. The solution is then filtered from the coal which is then washed and heat dried under low pressure. Most of the free sulfur is volatized from the coal due to the heat drying; additional free sulfur can be removed by additional washing and heat drying and/or solvent extraction techniques. At least 60 percent of the pyrite sulfur and pyrite iron is removed using the process of this invention. If desired, the ferrous chloride can be regenerated; this permits iron oxide to be recovered as a byproduct.

Unite Statesv Meyers atent 1 REMOVAL OF PYRITIC SULFUR FROM COAL USINGSOLUTIONS CONTAINING FERRIC IONS [21] Appl. No.: 163,893

Related US. Application Data Continuation-impart of Ser. No. 116,262,Feb. 17, 1971, abandoned.

[ 1 Oct. 30, 1973 3,652,219 3/1972 Peters et al. 23/200 3,640,016 2/1972Lee 44]] R 2,592,580 4/1952 Loevensteim. 23/200 1,980,809 11/1934 Levy23/226 Primary ExaminerC. F. Dees AttorneyDaniel T. Anderson et al.

[57] ABSTRACT Finely divided coal or solid coal derivatives containingpyrite are reacted with a ferric ion solution; FeCl is particularlysuitable. The ferric ion is reduced to ferrous ion and free sulfur isformed. The solution is then [52] Egg/ 2 47 filtered from the coal whichis then washed and heat [51] Int Cl b 9/00 dried under low pressure.Most of the free sulfur is [58] Fe. 44,4 6 volatized from the coal dueto the heat drying; addi gg z gg' 'a 7 3 tional free sulfur can beremoved by additional washing and heat drying and/or solvent extractiontechniques. At least 60 percent of the pyrite sulfur and pyrite iron isremoved using the process of this inven- [56] References cued tion. Ifdesired, the ferrous chloride can be regener- UNITED STATES PATENTSated; this permits iron oxide to be recovered as a by- 2,204,148 6/1940Nelms 44/4 X product. 2,895,796 7/1959 Hill 23/224 3,252,769 5/1966Nagelvourt 44/1 R 19 Claims, 2 Drawing Figures H2O Q H20 1 T f l 2 F90FeCl SOLUTION .neclmn 0 WATER filmy av coourLe fiaklzmosi A 212F 02 212F2 l 2 1 3518mm "20 Q F 1 ATM 5316:1014

Fe o

PYRITE o Flcla MAKE-UP COM 1 AT COAL FILTRATION I PATENIEnum 30 ms SHEET1 [IF 2 H2O Q H 0 2| T T 20 T I9) 'a FeCl WATER Y SOLUTION PREC PITATIONREHEAT Y COQUNG YKPTORIZATION i v 21m 2I2F I55F 22 I 23 R0 2 -H QXIATION .c All ATM SOL ION ll wane J10 Y REACTION FeCl -MAKE UP I AM 4COAL COAL m FILTRAYTION 0.5 HR

' Fig. I.

I N VEN TOR.

AGENT PATENIEU 0m 30 ms SHEET 2 OF 2 I4 15 FOUR smse COAL WASHING SULFURCOOLING CONDENSATION 225F MEDIA- l7 E Q G SULFUR N VAPORIZATION v 1 'AYM1 ATM COAL 2I2F 450% Fig- 2 Robert A. Meyers INVENTOR.

AGENT REMOVAL OF PYRITIC SULFUR FROM COAL USING SOLUTIONS CONTAININGFERRIC IONS This application is a continuation-in-part of applicationSer. No. 116,262 filed Feb. 17, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the removal ofpyritic sulfur from coal and solid coal derivatives and morespecifically to the solvent extraction of sulfur from pyrites in coalusing a solution containing a ferric ion.

The present use of coal in the United States is primarily for thepurpose of conversion into electrical energy and thermal generatingplants. One of the principal drawbacks in the use of United States minedcoal is due to their sulfur contents which can range up to percent.

Based on a 4 percent surface content, a 1,000,000 Kilowatt plant burnsabout 8,500 tons per day of coal and consequently emits 680 tons per dayof sulfur dioxide. If this sulfur could be removed and converted, itwould produce 900 tons of H 80, daily.

It has long been recognized that S0 in the atmosphere will either retardgrowth or kill vegetation. In addition, the potential hazard to humansappears about the same as for thevegetable kingdom.

While it is possible to remove pyritic sulfur from coal by frothflotation or washing processes; these are not selective so that a largeportion of the coal is discarded along with ash and pyrite. Hence, thesolution so far has been to simply burn coal having a low sulfurcontent. However, many pollution control districts now prohibit the useof coal having an excess of 1 percent sulfur. The result has been toseverely restrict the use of many United States coals, 90 percent ofwhich average about 2.5 percent contained sulfur. This has lead to theimportation of low sulfur content fuel oils for domestic and industrialuse. The crude oil reserves, which are the source of the residue, areexpected to run out in 20 30 years while coal reserves are sufficientfor several hundred years at a minimum.

It is, therefore, an object of this invention to provide a process forthe reduction of sulfur, particularly pyritic sulfur in coal. I

Another object is to provide a process for the recovery from coal ofsulfur and sulfur compounds.

Another object is to provide a process for the recovery of iron valuesfrom coal containing pyrite.

Other objects of this invention will become apparent from thedescription and the diagram to follow.

According to the invention, it has been found that it is possible toreact the pyrite contained in the coal with a solution containing aneffective amount of ferric ion to obtain a high yield of free sulfur. Feion particularly as F eCl is preferred; other ferric salts such asacetate, sulfate, citrate, oxide, ferric ammonium sulfate, etc., may beemployed. A typical reaction proceeds as follows:

2 FeCl FeS 3FeCl 25.

The solution containing some free sulfur, ferrous chloride and anyunc'onsumed ferric chloride is removed from the coal by filtration.

The coal is then washed and dried, preferably by heating in a vacuum;this results in the major portion of free surfur being volatized asfollows: S.Coal S coal. If desired, a further wash, filtration andheating will remove more of the sulfur and any residual ferrous ion. Oneor more extractions'with a suitable organic sulfur'solvent such asbenzene, kerosene or para cresol may be employed to further reduce thesulfur content of the coal.

Regeneration of the unused ferric chloride and ferrous chloride solutionmay be accomplished by first concentrating the solution by evaporatingmost of the water. The concentrated solution is cooled, therebyprecipitating the ferrous chloride from the ferric chloride, most of thelatter still remaining in solution. The precipitated ferrous chloride isair oxidized to ferric chloride and iron oxide and finally the ferricchloride is recycled and the iron oxide recovered.

Typical treatment temperatures may vary from 50 C C. Reflux times aretypically one-half 2 hours and higher. Typical coal particle sizes mayvary from 200 mesh to one-half-inch pieces. Atmospheric pressure may beemployed, but higher pressures can also be used.

The effective amount the ferric ion solution employed for extractiondepends on the amount of coal treated and its pyritic sulfur content,the amount of sulfur desired to be extracted, extraction times,extraction temperatures, concentration of the ferric ion in thesolution, etc.

The reaction of ferric chloride and ferrous persulfide to produce freesulfur is known. However, it was unexpected that the reaction withferric ion (e.g., FeCl and pyrite could be carried out in a coal mediumsince pyrite is dispersed very finely throughout the coal matrix, andpenetration of such an organic matrix with water is known to bedifficult. Furthermore, the volatization of sulfur from coal is unusualsince it well might be expected that the free sulfur would recombineeither with iron or with the coal upon heating. It is also well knownthat iron pyrites may be oxidatively dissolved from the coal matrix withstrong aqueous oxidizing agents such as HNO H 0 or HOCl. This willconvert the sulfur content to sulfate, but not to free sulfur. This isthe basis for chemical analysis of the pyritic sulfur content of coal;however, such strong oxidizing agents also extensively oxidize theorganic coal matrix. By contrast, ferric salts are almost totallyselective in the sense that the organic coal matrix is undisturbed.-

Hence, ferric salts, but not I-INO H 0 or l-IOCI, provide an economicalroute to the removal of pyrites from coal.

Coals which may be employed in this invention include those which areconsidered as coals in the popular or commercial sense, such asanthracites, charcoal, coke, bituminous coals, lignites, etc. Inaddition, chars from hydrocracked coals and middlings are all capable ofbeing refined by the extraction process of this invention.

The invention will be understood by reference to FIGS. 1 and 2 in whichferric chloride make-up solution and coal are fed into a pyrite reactor10 maintained at atmospheric pressure and about 212 F. Pyrite (FeS isextracted from the coal, and the slurry containing unreacted ferricchloride, ferrous chloride, sulfur, ferrous persulfide, and the treatedcoal are fed to a coal filtration unit 11. Vacuum disk filters in thecoal filtration unit are used to separate the bulk of the iron chloridesolution from the treated coal.

In the coal washing sections 12, 13, 14, and 15, four stages ofcountercurrent washing with intermediate filtration steps are used toreduce the residual chloride content of the coal to less than about 100ppm. A suitable residence time of the coal in each of the washing stagesis about l5 minutes; rotary vacuum disk filters FeCl 3/2 4FeCl Fe O Thereaction employs air and is carried out at atmospheric pressure at about480 F. The oxidized precipitate (ferric chloride and iron oxare used to,separate the coal and wash the Solunon ide) is then transferred to asolution-filtration unit 23 tween washmg where the soluble ferricchloride is then separated from The washed coal then fed to a coal drymgm 16 the insoluble iron oxide by dissolving in water. The ferwhere steamtube dryers are employed E ric chloride solution is recycled to theferric'chloride the ljesldual ,water from the washe d coal thls make-upsolution for use in reactor 10. The iron oxide erauon being earned outat atmosPhenc pressure and is filtered from the ferric chloride solutionand may be about 212 F. The heated dry coal is then forwarded tog.ecovemd as a byproduct of the process a sulfur vaporization unit 17where freesulfur, which Typical coals which may be employed in theprocess was produced in the extraction reaction in reactor 10, includeMissouri Lower Freeport, Bevier, Indiana No is vaporized at atmosphericpressure and a temperature V, and Pittsburgh. These coals contain sulfurforms as of about 2 F under reducfgd (30 min) shown in Table l whenfreshly mined. As they stand exand i 250 9 The vaponzed sulfur 1sremoved posed to air, small amounts of sulfate sulfur are formed bynitrogen gas into a sulfur condensation unit 18 and from the pyritecontent. cooled to about 225 F causing it to condense. The sulfur vaporis then passed to a recovery unit as bright sul- TABLE 1 fur. Thetreated coal with reduced pyrite content is SULFUR COMPOUNDS IN COALthen forwarded for use.

in the ferric chloride regeneration stage, the filtrate Bevier gigIndiana No v Pittsburgh from the coal filtratlon unit 11 15 passed to athickener p i unit 19 where water is vaporized from the solution at12-33 0.5-L7 atmospheric pressure and about 212 F. The concen- LL23 L543trated solution is then passed to a precipitation unit 20 Total whereferrous chloride is precipitated by cooling the solution to 155 F atatmospheric pressure. Unreacted Table 2 shows the original pyriticsulfur content of ferric chloride solution from the precipitation unit20 the Missouri and Lower Freeport coals and the reducis heated in areheater 21 and then combined with fer- 3 tion in sulfur content due totreatment of FeCl;,. ric chloride make-up for feeding to the reactor 10.It will be observed that a marked reduction in pyritic The ferrouschloride precipitate, which has been sepsulfur occurs after only asingle treatment with FeCl arated by filtration from the ferric chloridesolution in followed by a water washing and drying. reactor 20, istransferred to an air oxidation furnace 22 Table 3 shows the effect ofemploying an organic solwhere it is reoxidized back to ferric chlorideand iron vent to remove the free sulfur which remains following oxide,the reaction equation being the FeCl and water washing treatment.

TABLE 2 FeCls extraction data Wt. loss after Reflux washing Pyritic 2 Fe3 (90 C.) and dry- Sulfur Wt pcrsulfur Sample Wt. Vol. Molarity, pyritictime ing, wt. Eschka, wt. eent Fe removed,

Coal number coal, g. 3 FeOh FeCl; Fe (hrs.) percent 5 percent. in coal 2percent Missouri untreated (mesh size -200) 4. 75 1. 65

Missouri (mesh size 200) 1 200 0.5 3.9/1 16 0.22

Missouri (mesh size 200) 2 500 0.3 5/1 2 -9.1 4.18 0.86

Missouri (mesh size 200) 3 30 500 0.5 13/1 20 +2.0 3.2; 0.19

Lower Freeport U. (Mesh size -14) 54 16 Lower Ireeport (mesh size -14) 450 730 0.5 6/1 3 2 4 l4. 1 1. 99 1.10

1 ASTM D271.

2 Bureau of Mines procedure and Standard Methods of Chemical Analysis,Furman, volume 1, page 542. 3 Remarks: Residue removed from condenserwas analysed by electron microprobe as follows: Fe, S, Si, O, C weremaior constituents; Ca, 01, A1

were trace.

Yellow crystals formed; Hg spot test for free S was positive.

6 Sample 2 was washed once with 250 cc. hot water and dried 24 hours ina hot water and dried 72 hours at 90 in a vacuum oven.

0. vacuum oven. Samples 3 and 4 were washed twice with 250 cc.

TABLE 3 Solvent extraction data following FeCla treatment and water washSulfur concentration Percent Wt. loss, extrac- Sample number SolventExtraction procedure gain Esehka tion 1 Benzene, 5-10 min 3 hot (80 C.)cc. washings 8L 2 -.do -.do o i g: 60 3a -410 "do +2 2 3g so 3bp-Cresol, 510 min. M111. (200 C.) reflux 13.6%{ 4 Benzene, 5-10 min. 3hot (80 C.) 100 cc. washings g 74 From the data in Table 3, it appearsthat the organic solvent treatment causes a major portion of the pyriticsulfur to be extracted; also, use of para cresol appears to result inextraction of organic as well as pyritic bound sulfur. While theefficiencies shown range from 60 percent to at least 89 percent, thisefficiency range can be changed by altering such factors as wash times,particle size, amounts and concentrations of FeCl;, and solvents, ferricsalt treatment, reflux temperature, etc.

Table 4 shows the effect of FeCl;, extraction on various coals employingreaction conditions similar to Table 2. The table shows that 72 93percent of the pyritic sulfur content may be removed in 2 hours by 0.5 Mrec], solution from a wide variety of coals. Further, the process wasapplicable to all the coals, and in the case of Indiana No. V, theextraction efficiency was excellent.

TABLE 4 PYRITIC SULFUR REMOVAL DATA Pyritic Total Total Total SulfurSulfur Sulfur Sulfur Coal Removed Removed Before After Lower Freeport.48 75 3.87 2.0l Lower Freeport 64 72 3.40 1.2 3 Bevier 36 72 4.60 2.94Indiana No. V 51 93 3.28 1.67 Pittsburgh 39 78 L81 l. l0

All coals were 14 mesh except Bevier which was 200 mesh The process ofthis invention is extremely efficient in that at least 60 percent of thepyrite sulfur is extracted and the iron employed for extraction iseasily recovered (about 85-90 percent) and may be reused. Furthermore,iron removal is facilitated since the iron contained in the FeClextraction solution and the iron in the pyrite are indistinguishable;hence, no special techniques are required to separate different metalsfrom the wash-extraction operation if metal recycling isdesired.

in addition, the process is simple in that no high temperatures,pressures or catalysts are required.

Finally, the extraction with FeCl does not produce an interaction withthe organic coal matrix; this permits substantially all of the coal tobe utilized as low sulfur fuel.

What is claimed is 1. A process for reducing the pyritic sulfur contentof 7 coal which comprises reacting the coal with an effective amount ofan aqueous solution containing F e ion and removing from the coal sulfurformed by the pyrite reaction.

2. A process for reducing the pyritic sulfur content of coal whichcomprises reacting the coal with an effective amount of an aqueoussolution containing Fe ion selected from the class consisting of FeCl:,and ferric sulfate, and removing from the coal sulfur formed by thepyrite reaction.

3. A process for reducing the pyritic sulfur content of coal whichcomprises:

reacting the coal with an effective amount of an aqueous solutioncontaining Fe ion;

removing from the coal sulfur formed by the pyrite' reaction using thefollowing steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the treated coal;and

drying the coal to volatize the free sulfur contained therein.

4. The process of claim 3 in which free sulfur from the volatizationstep is extracted with an organic solvent for sulfur selected from theclass consisting of benzene, kerosene a'nd p-cresol.

5. The process of claim 3 in which the aqueous solution employed isselected from the class consisting of FeCl;; and ferric sulfate.

6. The process of claim 3 in which the aqueous F e ion solution isselected from the class consisting of ferric acetate, ferric citrate,ferric oxide and ferric ammonium sulfate.

7. A process for reducing a pyritic sulfur content in coal whichcomprises:

reacting the coal with an effective amount of an aqueous solutioncontaining Fe ion and removing from the coal sulfur formed by the pyritereaction using the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the coal; and

extracting free sulfur from the treated coal with an organic solvent forsulfur selected from the class consisting of benzene, kerosene andp-cresol.

8. The process of claim 7 in which the aqueous solution employed isselected from the class consisting of FeCl and ferric sulfate.

9. The process of claim 7 in which the aqueous Fe ion solution isselected from the class consisting of ferric acetate, ferric citrate,ferric oxide and ferric ammonium sulfate.

10. A process for reducing the pyritic sulfur content in coal whichcomprises:

reacting the coal with an effective amount of ,an

aqueous solution of Fe ion, and removing from the coal sulfur formed bythe pyrite reaction using the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the treated coal;

drying the coal to volatize the free sulfur contained therein; and

oxidizing the separated solution to ferric ion.

11. The process of claim 10 in which the oxidizing step is carried outwith a gas selected from the class consisting of air and oxygen.

12. The process of claim 10 in which the aqueous solution employed isselected from the class consisting of FeCl;, and ferric sulfate.

13. The process of claim 10 in which the aqueous Fe ion solution isselected from the class consisting of ferric acetate, ferric citrate,ferric oxide and ferric ammonium sulfate.

14. A process for reducing the pyritic sulfur content in coal whichcomprises:

reacting the coal with an effective amount of an aqueous solution Feion, and removing from the coal sulfur formed by the pyrite reactionemploying the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the treated coal;

drying the coal to volatize the free sulfur contained therein;

extracting additional free sulfur from the treated coal with an organicsolvent for sulfur selected from the class consisting of benzene,kerosene and p-cresol;

concentrating the ferrous ion solution by evaporating some of the water;

cooling the solution thereby precipitating ferrous ion;

separating the ferrous ion precipitate from the solution containingferric ion;

oxidizing the ferrous ion precipitate to ferric ion and iron oxide;

dissolving the ferric ion in water; and

separating the iron oxide from the aqueous solution containing ferricion.

15. The process of claim 14 in which the aqueous solution employed isselected from the class consisting of FeCl;, and ferric sulfate.

16. The process of claim 14 in which the aqueous Fe ion solution isselected from the class consisting of ferric acetate, ferric citrate,ferric oxide and ferric ammonium sulfate.

17. A process for reducing the pyritic sulfur content in coal whichcomprises:

reacting the coal with an effective amount of an aqueous solution of Feion and removing from the coal sulfur formed by the pyrite reactionusing the following steps:

separating the said solution from the treated coal;

lution employed is selected from the class consisting of FeCl and ferricsulfate.

19. The process of claim 17 in which the aqueous Fe ion solution isselected from the class consisting of ferric acetate, ferric citrate,ferric oxide, and ferric ammonium sulfate.

2. A process for reducing the pyritic sulfur content of coal whichcomprises reacting the coal with an effective amount of an aqueoussolution containing Fe 3 ion selected from the class consisting of FeCl3and ferric sulfate, and removing from the coal sulfur formed by thepyrite reaction.
 3. A process for reducing the pyritic sulfur content ofcoal which comprises: reacting the coal with an effective amount of anaqueous solution containing Fe 3 ion; removing from the coal sulfurformed by the pyrite reaction using the following steps: separating thesaid solution from the treated coal; washing the coal and separating thewash solution from the treated coal; and drying the coal to volatize thefree sulfur contained therein.
 4. The process of claim 3 in which freesulfur from the volatization step is extracted with an organic solventfor sulfur selected from the class consisting of benzene, keRosene andp-cresol.
 5. The process of claim 3 in which the aqueous solutionemployed is selected from the class consisting of FeCl3 and ferricsulfate.
 6. The process of claim 3 in which the aqueous Fe 3 ionsolution is selected from the class consisting of ferric acetate, ferriccitrate and ferric ammonium sulfate.
 7. A process for reducing a pyriticsulfur content in coal which comprises: reacting the coal with aneffective amount of an aqueous solution containing Fe 3 ion and removingfrom the coal sulfur formed by the pyrite reaction using the followingsteps: separating the said solution from the treated coal; washing thecoal and separating the wash solution from the coal; and extracting freesulfur from the treated coal with an organic solvent for sulfur selectedfrom the class consisting of benzene, kerosene and p-cresol.
 8. Theprocess of claim 7 in which the aqueous solution employed is selectedfrom the class consisting of FeCl3 and ferric sulfate.
 9. The process ofclaim 7 in which the aqueous Fe 3 ion solution is selected from theclass consisting of ferric acetate, ferric citrate and ferric ammoniumsulfate.
 10. A process for reducing the pyritic sulfur content in coalwhich comprises: reacting the coal with an effective amount of anaqueous solution of Fe 3 ion, and removing from the coal sulfur formedby the pyrite reaction using the following steps: separating the saidsolution from the treated coal; washing the coal and separating the washsolution from the treated coal; drying the coal to volatize the freesulfur contained therein; and oxidizing the separated solution to ferricion.
 11. The process of claim 10 in which the oxidizing step is carriedout with a gas selected from the class consisting of air and oxygen. 12.The process of claim 10 in which the aqueous solution employed isselected from the class consisting of FeCl3 and ferric sulfate.
 13. Theprocess of claim 10 in which the aqueous Fe 3 ion solution is selectedfrom the class consisting of ferric acetate, ferric citrate and ferricammonium sulfate.
 14. A process for reducing the pyritic sulfur contentin coal which comprises: reacting the coal with an effective amount ofan aqueous solution Fe 3 ion, and removing from the coal sulfur formedby the pyrite reaction employing the following steps: separating thesaid solution from the treated coal; washing the coal and separating thewash solution from the treated coal; drying the coal to volatize thefree sulfur contained therein; extracting additional free sulfur fromthe treated coal with an organic solvent for sulfur selected from theclass consisting of benzene, kerosene and p-cresol; concentrating theferrous ion solution by evaporating some of the water; cooling thesolution thereby precipitating ferrous ion; separating the ferrous ionprecipitate from the solution containing ferric ion; oxidizing theferrous ion precipitate to ferric ion and iron oxide; dissolving theferric ion in water; and separating the iron oxide from the aqueoussolution containing ferric ion.
 15. The process of claim 14 in which theaqueous solution employed is selected from the class consisting of FeCl3and ferric sulfate.
 16. The process of claim 14 in which the aqueous Fe3 ion solution is selected from the class consisting of ferric acetate,ferric citrate and ferric ammonium sulfate.
 17. A process for reducingthe pyritic sulfur content in coal which comprises: reacting the coalwith an effective amount of an aqueous solution of Fe 3 ion and removingfrom the coal sulfur formed by the pyrite reaction using the followingsteps: separating the said solution from the treated coal; washing thecoal and separating the wash solution from the treated coal; dRying thecoal to volatize the free sulfur contained therein; concentratingferrous ion solution by evaporating some of the water; cooling thesolution therein by precipitating the ferrous ion; separating theferrous ion precipitate from the solution containing ferric ion; airoxidizing the separated solution to ferric ion and iron oxide;dissolving the ferric ion in water; and separating the iron oxide fromthe aqueous solution containing ferric ion.
 18. The process of claim 17in which the aqueous solution employed is selected from the classconsisting of FeCl3 and ferric sulfate.
 19. The process of claim 17 inwhich the aqueous Fe 3 ion solution is selected from the classconsisting of ferric acetate, ferric citrate and ferric ammoniumsulfate.